[ There's quite a few things Harold is about to say here, and they all get erased by Jayce's last comment. He stares at him, aghast. Difficult student, was it? Harold is someone who, with great caution, changed the entire world. He doesn't think they're incompatible at all. ]

Mr. Tallis, [ he says sternly, ] do not inject yourself with anything that has been programmed with code written on paper.

[ He lets that stand for a solid second as an absolute Jayce needs to internalize. ]

I don't object to using yourself as a test subject, but we will not approach it with death as an acceptable outcome. [ That's also an absolute for Harold, even in this case. Death means losing a memory here, which is uniquely horrifying to him. ]